Deposition and Dissipation Dynamics of Thidiazuron in Cotton Leaf and Soil
A QuEChERS liquid chromatography analysis method was established for the determination of thiamethoxam in cotton leaves and soil and the residual and degradation dynamics of 50%thiamethoxam wettable powder,and 55%thiamethoxam suspension after foliar spraying on cotton leaves and soil were studied.And then the field experiment was conducted by applying 2 times of the recommended dosage(600 g/hm2)and 3 times of the recommended dosage(900 g/hm2)once each,and sampling and testing were conducted.The samples of thidiazuron were extracted by acetonitrile,cleaned up by 50 mg C18 and detected by liquid chromatography.The results showed that the linear relationship between mass concen-tration and peak area was good in the concentration range of 0.10-50.00 mg/L(R2>0.9999);At 0.50,1.00,5.00 and 15.00 mg/L spiking levels,the average recoveries of thidiazuron were 95.13%-101.02%with the relative standard deviation(RSD)of 0.62%-2.71%,the detection limit(LOD)were 0.0056,0.0043 mg/kg and the limit of quantitation(LOQ)were 0.0672,0.0523 mg/kg,which met the requirements of the residual test.The results of the digestion dynamic test indicated that:the residual digestion laws of th-iapenon were in accordance with the first-order kinetic equation.Different formulations and doses of thidi-azuron showed differences in original deposition and dissipation rates in leaves and soil.Half-lives(T1/2)of thidiazuron was 2.24-3.76 d and 4.70-6.04 d,with faster dissipation,and it belonged to the easily-degraded pesticides.After 21 days of application,the residual levels of thidiazuron were lower than the national maximum residue limit(MRL)of 1 mg/kg,respectively,indicating a low residue risk of the pesticides.
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